Class II restriction endonucleases are endodeoxyribonucleases, which are able to recognize and cleave certain DNA nucleotide sequences. One phosphodiester bridge is hydrolyzed in each polynucleotide chain of the target sequence. Class II restriction endonucleases are valuable for the analyses of DNA molecules. Specific Class II restriction endonucleases are admittedly already known for numerous recognition sequences. However, their accessibility is often unsatisfactory. In many cases the microorganisms from which the restriction endonucleases are isolated are difficult to cultivate or pathogenic. In addition, the yield is low on large-scale production.
The restriction endonuclease SacII, as described in Gene 47: 1-153 (1986), cleaves DNA at the same position as does the invention. SacII, however, does not cleave DNA sequences containing methylated cytosine at its recognition point. Additionally, SacII is very difficult to separate from related endonuclease SacI, and the yields obtained are very low.
Therefore it is an object of the present invention to provide an isoschizomer for SacII the production of which is simpler and of higher yield and which differentiates between methylated and non methylated DNA sequences.